To characterize the variability in GRS 1716–249 during both epochs E1 and E2, the power density spectrum (popularly known as PDS) was generated. They are displayed in Fig. REF . PDS are generated by using the Fourier transform of the light curves. The peaks in the PDS correspond to the presence of periodic signals in the light curves. The powspec tool distributed as XRONOS sub-package of the heasoft package is used to generate the PDS. The NuSTAR detectors are affected by dead-time, which is \(\approx \)  2.5 ms [1]}, [2]}. However, we generated PDS for FPMA and FPMB separately, which are not dead-time corrected. The presence of dead-time affects the contribution of white noise in the PDS and sometimes affects the overall shape of the QPO, but there is no effect on the QPO peak frequency. A distortion of the overall QPO shape affects the Q-factor and significance, but the variation is only significant at higher count rates, above \(\sim \) 600 counts/sec [2]}. We observed a QPO in both detectors. The PDSs were fitted with a model consisting of two Lorentzians added together. The first, broader Lorentzian component represents the continuum, whereas the second Lorentzian was used to fit the QPO. The significance of the QPOs was estimated by the ratio of the area under the Lorentzian profile peaking at the QPO frequency (shown with the blue dash-dot-dashed line in Fig. REF ) to the 1\(\sigma \)  negative error in the area estimated by the model. The recipe suggested by [4]} was adopted to calculate the confidence level of the detected QPO and to reject low significance peaks.
